Download COMPOSITION OF THE GRAM-POSITIVE PLASMA MEMBRANE

COMPOSITION OF THE GRAM-POSITIVE PLASMA MEMBRANE
Protein ( 65%; large range [>200] distinct protein species present)
Lipid ( 25%; mainly phospholipid; 3-4 major types present)
Lipoteichoic acid (5-10%)
MAJOR PHOSPHOLIPID HEADGROUP (X) SPECIES IN BACTERIA
-X
PHOSPHOLIPID
-H
Phosphatidic acid (PA)
-CH2-CH2-NH2
Phosphatidyl ethanolamine (PE)
-CH2-CH-NH2
CO2H
Phosphatidyl serine (PS)
-CH2-CH-CH2
OH OH
Phosphatidyl glycerol (PG)
O
-CH2-CH-CH2-O-P-OOH
O
CH2 O
CH-O-C-R1
CH2-O-C-R2
O
Diphosphatidyl glycerol/Cardiolipin
(diPG/CL)
(R1 & R2 = long [ C16] acyl chains)
FUNCTIONS OF GRAM-POSITIVE PLASMA MEMBRANE
1.
3.
4.
6.
8.
9.
Highly selective permeability barrier. 2. Concentrative solute transport.
Oxidative phosphorylation and electron transport.
Biosynthesis of peptidoglycan. 5. Biosynthesis of teichoic/teichuronic acids.
Biosynthesis of lipoteichoic acids. 7. Biosynthesis of capsular polysaccharides.
Biosynthesis of phospholipids. 8. Translocation and processing of exported proteins
Chemosensing and transmembrane signaling. 10. Chromosome anchoring.
COMPOSITION & FUNCTIONS OF GRAM-VE PLASMA (INNER) MEMBRANE






Protein and phospholipid composition generally similar to that of Gram+ves BUT
Lipoteichoic acids NOT found
Functionally similar to Gram+ve plasma membrane BUT
No biosynthesis of wall teichoic acids or membrane lipoteichioc acids.
Biosynthesis of lipopolysaccharides and membrane-derived oligosaccharides
Additional transport system (osmotic shock sensitive [periplasmic] transport
system)
COMPOSITION OF THE (GRAM-VE) PERIPLASM
Water soluble proteins
Low-molecular-weight carbohydrate “membrane derived oligosaccharides (MDO)”
(Peptidoglycan layer)
FUNCTIONS OF THE (GRAM-VE) PERIPLASM
1.
2.
3.
4.
5.
6.
Nutrient degradation (phosphatases, carboxypeptidases)
Nutrient transport (specific periplasmic binding proteins)
Electron transport (denitrifying and chemolithotrophic bateria)
Elimination of foreign DNA (restriction endonucleases)
Modification of potentially toxic compounds (-lactamase; aminoglycoside 3’
phosphotransferase)
Maintain iso-osmolarity across the plasma membrane (MDO)
[P-glycerol]1-4

EtNP-[Glucose]8-10

O-succinate
Fig. 17. Membrane-derived oligosaccharide (MDO).
EtNP = phosphoethanolamine. Note that glycerol
phosphate and succinate both carry –ve charges.
COMPOSITION OF THE GRAM-VE PEPTIDOGLYCAN LAYER
Peptidoglycan (relatively thin 2nm)
Covalently bound lipoprotein
O
R1-C-O-CH2

R2-C-O-CH
diglyceride
O

CH2

S
thioether linkage

CH2
O

R3-C-N-C-C-{56 amino acids}-Lys(58)-Diaminopimelic acid (of peptidoglycan)
H HO
Fig. 18. The Braun lipoprotein of E. coli. The N-terminal cysteine (Cys1) residue is
modified by the attachment of amide-linked fatty acid (R3-CO) and thioether-linked
diglyceride. The three fatty acyl groups interdigitate into the inner leaflet of the outer
membrane whilst the C-terminal lysine (Lys58) is amide-linked to the DAP of
peptidoglycan. Thus, the Braun lipoprotein effectively anchors the outer membrane to
the underlying murein (see Fig. 19 & 20).